Envoy 2WD V6-4.3L VIN W (1998)
The VCM has the ability to monitor this process by using the Bank 1 Sensor 1 and the Bank 1 Sensor 3 heated oxygen sensors. The Bank 1 Sensor 1
sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The Bank 1
Sensor 3 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the ability of the catalyst to
convert the exhaust gases efficiently. If the catalyst is operating efficiently, the Bank 1 Sensor 1 sensor will produce a far more active signal than that
produced by the Bank 1 Sensor 3 sensor.
The HO2S sensors which are used in order to monitor the catalyst function are the same as the HO2S sensors which are used in order to control the fuel.
Bank 1 Sensor 1 and Bank 1 Sensor 3 are used primarily for catalyst monitoring. These sensors also play a limited role in fuel control. If a sensor output
indicates a voltage either above or below the 450 millivolt bias voltage for an extended period of time, the VCM will make a slight adjustment to the fuel
trim in order to ensure that the fuel delivery is correct for catalyst monitoring.
